Deflecting particles in vacuum coating process



March 12, 1968 M. (3. PAUL ET AL 3,373,050

DEFLECTING PARTICLES IN VACUUM COATING PROCESS Filed Dec. 50. 1964 AA.C. GAS 56 SUPPLY SUPPLY SOURCE INVENTORS I MAYNARD 6. PAUL PAUL E.OBERG BY I W -W AGENT United States Patent 3,373,050 DEFLECTINGPARTICLES IN VACUUM COATING PROCESS Maynard C. Paul and Paul E. Oberg,Minneapolis, Minn.,

assignors to Sperry Rand Corporation, New York, N.Y-,

a corporation of Delaware Filed Dec. 30, 1964, Ser. No. 422,161 9Claims. (Cl. 117-106) ABSTRACT OF THE DISCLQSURE The use of a jet ofinert gas in a thin film vacuum dep- OSlllOl'l apparatus to separateunduly large particles which may spatter from the melt from theevaporant to be deposited on the substrate.

The present invention relates generally to the evaporative fabricationof thin films in an evacuated chamber and more particularly to a methodand apparatus for causing an evaporated material to deviate from itsexpected evaporant path.

The evaporative fabrication of a film of material within an evacuatedchamber is a techniquethat has recently been employed in the electronicsindustry for fabricating electrical apparatus, such as, integratedcircuits. Conventional integrated circuits usually are composed ofseveral layers of electrically conductive films which in most instancesare insulated from one another. Conventionally, the electricallyconductive films and the electrically insulating films are formed withinthe evacuated chamber by vapor deposition techniques. Generallysuccessful circuit design depends, in some degree, in each of thedeposited layers having desirable uniform characteristics.

it has been found that when certain materials are employed to performone or the other of the conductive or insulating functions of theselayers it becomes difficult to consistently attain films exhibiting thedesired uniformity. A major difficulty results from the low thermalconductivity of certain non-conductive materials, such as siliconmonooxide, which, when heated develops unevenly hot areas which resultin spattering. Spattering is characterized by the sudden ejection fromthe material being evaporated of solid or liquid particles. Althoughmetals do not generally exhibit the problem of spattering during theirthermal evaporation, some difiiculty has been experienced when workingwith certain types of metals, for example, cadmium, zinc and magnesium.These large particles tend to cause pin-hole flaws in the depositedlayer.

In the past, in order to reduce spattering, evaporation sources havebeen adapted to provide a structural arrangement for causing anevaporant to ascend to a substrate member by following a diverse pathfrom its source. For effecting such diverse path, bafile plates havebeen interposed between the material in the evaporating container andthe substrate upon which the evaporant is intended to be deposited. Thebaflle is effective to prevent the free flow of vapor between the battleand the substrate by cutting off straight line paths between thematerial and the substrate. Spattering particles are trapped on thebaffle surface whereupon they may be retained or subsequentlyre-evaporated therefrom. A batlle arrangement, however, for preventingthe formation of nonuniform films, is often undesirable in that it cancause a reduction in evaporation rate and can become clogged bycondensing vapor.

The formation of certain films such as metal oxides must often beaccomplished by depositing the metal film and simultaneously orsubsequently heating the entire sub- 3,373,050 Patented Mar. 12, 1968strate and any previously deposited films on the substrate to a hightemperature in an oxygen atmosphere-a process which can lead to possibleharmful effects on the substrate or on previously deposited films.

It is therefore an object of the invention to provide an improved methodof evaporatively fabricating thin films of materials.

It is another object of the present invention to provide apparatus forreducing the effect of source spattering upon the deposited film layers.

It is a still further object of the present invention to provideapparatus which is effective to reduce the effect of source spatteringupon the deposited film without impeding the evaporant path.

It is a still further object of the present invention to provide amethod for separating mixed material in an evaporant.

It is yet another object of the invention to provide an improvedapparatus for permitting the evaporative fabrication of both metallicand non-metallic films.

Yet another object of the invention is to provide a means of depositingfilms without influencing their properties by thermal effects caused bydirect heat radiation onto the substrate from the vapor source.

Still another object of the invention is to provide a means ofdepositing certain homogeneous films of different composition from thatof the vapor source without subjecting the substrate and/or anypreviously deposited films to possible undesirable treatment.

The above and other objects are accomplished in accordance with themethod and apparatus of the present invention wherein there is providedvapor deposition apparatus which includes a gas introduction means forpermitting the introduction of selected gas or gases into the evacuatedchamber. The gas introduction means is arranged such that the gasemanating therefrom may be directed toward the evaporant path. Particlesof evaporant are caused to be deflected from their normal path by thegas molecules. A vapor or evaporant particle rising from the source isdeflected by a particle or gas molecule of the gas stream in accordancewith the velocities, masses, and directions of the particles. In thecase of vapor deposition of such materials as silicon monoxide, forinstance, spattered otf particles have a greater mass than theevaporated particles, and the spattered otf particles are not deflectedto the same degrees as the evaporated particles. By properly disposingof the substrate member within the apparatus, the deposition ofundesirable particles or spattered-01f pieces of the evaporant can beobviated. Accordingly, the resultant deposit would be free from thelarger spattered particles and thus would exhibit a relatively smooth,homogeneous surface.

The novel features of the invention, as well as additional objects andadvantages thereof, will be understood more fully from the followingdescription when read in connection with the accompanying drawing, inwhich:

The figure describes a vertical section of the bell jar enclosuretogether with system components.

The apparatus shown in the figure sets forth an embodiment of thepresent invention, and includes a base plate 12 supporting the bell jar10, which with gasket member 14 form an enclosure or chamber adapted tobe evacuated by any suitable vacuum pump (not shown) coupled to theapparatus via pipe 16. The base plate is in a preferred mannerconstructed of stainless steel and grounded as shown at 13.conventionally, the base plate is constructed of rigid material and thebell jar of glass. The material to be evaporated and subsequentlycondensed, that is, for example, the silicon monoxide melt 18, iscontained in the crucible 20 which is provided with a helically woundtungsten resistance heating coil 22 for the mouth of the source 20 sothat the islicon monoxide vapor cannot be deposited directly onto theSubstrate and so that heating of the substrate by radiation from thesource is minimized. As observed from the figure, the substrate ispositioned out of the line of sight of the melt 13. The crucible andshield are preferably constructed of tantalum which, as a refractorymaterial is capable of withstanding high temperatures as well asexhibiting low vapor pressure characteristics essential in a vacuumchamber to prevent contamination. The crucible and heating coilcooperate to form a treating means. Containers other than crucibles maybe employed to hold the material to be melted and heating means otherthan a resistance heated filament may be employed to heat the melt.Current for the heating element may be supplied by an external source 24by way of conductors 26 and 28 secured to conductive elements 36 in turnsecured to a bolt-like conductor plug 32 sealed to the base plate 12. byappropriate sealing means. Conductor 29 is a ground return from theresistance coil and is connected to table 19. It is not intended,however, that the conductor member 32 (plug) is to be limited to theparticular configuration illustrated inasmuch as a wide variety ofarrangements are suitable. The power output of the heater filament 22 iscontrolled either automatically or manually and the Output may becontinously varied, for example, from to 90% of maximum power. Crucibleis located on a table member 19 suitably positioned on the base plate12. Disposed to the left of the melt material 18 and in the upperportion of the bell jar is a substrate heater 34 provided with heatingelements 36, preferably made of tungsten, connected to leads 38 and 40and power supply means 42 via a bolt-like plug as aforementioned.Beneath the heater and adjacent thereto is a holder 44 for holding asubstrate 46 in a predetermined position. Conductor 43 connected toholder 44 provides a ground through support member 43. Various substratematerials may be used, the instant embodiment employing glass, and uponthis glass substrate, or upon layers previously formed upon this glasssubstrate, the evaporated material is allowed to condense in a designedmanner. A mask (not shown) may be used for defining one or more filmsand may be held in contact with, or at a predetermined distance from thesubstrate 46 by holder 44. The holder which supports the substrate 46,may be held in any convenient manner, as by the support 48. Thesubstrate holder may be designed to be adjustable to a variety ofpositions and is preferably constructed of stainless steel.

The normal evaporant path may be defined by a cone 50 projected from apoint slightly above the melt surface to the slag deposit shield 52. Theslag shield may be secured to the post 48 such as by bracket means 54 orby any other suitable means.

On the right-hand side of the vapor source and between the slag shield52 and the crucible, there is provided a gas introduction means 56. Thegas introduction means 56 includes a variable leak valve 58 in suitabletubing 59, pressure gauge means 60, and jet means 61 attached to a gassource 62. As representative of dimension, no limitation intended, thedistance between the upper edge of crucible 20 and the slag shield 52may be 18 inches, and the gas introduction jet is disposed in the belljar such that the stream of the gas particles intercepts the evaporantcone at a predetermined distance above the vapor source to produce thedesired deflection. The jet of gas emanating from the introduction meansis similarly described as or represented by a cone projected from theorifice of the introduction means through nozzle element 64 whichfunctions to direct the gas in a desired manner toward the evaporant.The nozzle configuration may be designed in accordance with one offeringthe desired result. The substrate 46 is angularly disposed with respectto the crucible 20 and located outside of the normal evaporant path andaccordingly evaporant is normally precluded from depositing onto thesubstrate.

It is also evident that by suitably adjusting the substrate by thesupport 48, spattering onto the substrate may be precluded. Normalevaporant travels in straight lines, and as observed in the figure, theevaporant cannot see the substrate because of the shield 23. However, itis still possible for spattering to occur, since a spattered particletravels in a trajectory due to gravity and hence may travel in anarc-like trajectory to the substrate. Hence a suitable adjustment of thesubstrate holder prevents the spattered particles from striking thesubstrate. The slag shield 52 is effective to prevent evaporant fromhaphazardly coating the upper portion of the bell jar and otherapparatus contained therein. in operation, the material 18 in theevaporation source 20 is heated by applying power from the supply means24 to heating element 22 and raising the temperature of the materialabove its vaporization point, for example, in the case of siliconmonoxide, to a temperature of approximately 1200 degrees centigrade.This is done while maintaining the pressure in the bell jar atapproximately 1 times 10 to the minus 6 millimeters of mercury. When thedesired evaporation temperature is reached, and it appears that suchtemperature has reasonably stabilized throughout the melt, a shuttermember 66 above the melt is rotated outside of the evaporant cone areaand the melt or evaporant is permitted to deposit on the slag shield 52.The shutter member 66 is mounted at one end upon a serrated gear portion68, such gear portion being integral with the shaft 70 which is turnedby applying a force to knob 72. Since any other suitable arrangement forthe shutter may be used, there is no intention to limit theconfiguration to the specific one illustrated. At this time the gasintroduction means 56 is permitted to cause a flow of gas to interceptthe evaporant. In the preferred embodirnents, argon gas is employed,although other inert gasses may be used in lieu thereof, such as xenon,krypton, neon, helium, or radon. Although the mass of the argon atom isslightly less than that of the silicon monoxide molecule, there issufi'icient momentum exchange for deflection of silicon monoxidemolecules to occur. Depending upon the velocity of the argon and siliconmonoxide streams, the deflected silicon monoxide emerges at an anglebetween the horizontal and vertical, but preferably strikes thesubstrate at a right angle to prevent angle of incidence effects duringdeposition.

Silicon monoxide films or layers deposited while utilizing the method ofthe present invention are free from spattered particles and are notinfluenced by heat radiated directly from the source or by varyingdeposition rates caused by clogging baflles which can be a problem whendepositing in the normal manner.

Additionally, an active gas such as oxygen can be used as the deflectingbeam resulting in the deposition of a different vapor such as SiOinstead of SiO. The process of deflecting the original vapor beamautomatically assures that a majority of the deflected particles comeinto contact with the deflecting beam particles resulting in ahomogenous deposited film of different composition from the originalvapor beam. The chemical reaction between the deflecting beam and theevaporant beam in the vapor before it reaches the substrate aids in theassurance that the resulting deposit upon the substrate is one of ahomogeneous nature. It i not necessary to heat the substrate excessivelyin order to promote the chemical reaction.

It is understood that suitable modifications may be made in thestructure as disclosed provided that such modifications come Within thespirit and scope of the appended claims. Having now, therefore, fullyillustrated and described my invention, what I claim to be new anddesire to protect by Letters Patent is:

What is claimed is:

1. The method of indirect vacuum deposition of an evaporant upon asubstrate comprising the steps of:

(a) heating a material within an evacuated enclosure to produce anevaporant,

(b) introducing a gas against the evaporant to thereby create a momentumexchange between the evaporant and the gas causing only evaporantparticles below a predetermined size to deflect and deposit upon saidsubstrate.

2. In a method of vacuum depositing a smooth homogenous layer ofevaporant free of larger particles of evaporant, the method comprisingthe steps of:

(a) locating a substrate within an evacuated enclosure above a treatingmeans and to one side of a conical path extending above an upper surfaceof said treating means,

(b) heating a deposition material to cause evaporation thereof asevaporant,

(c) introducing a gas stream against the evaporant at a predeterminedpoint along a path thereof to thereby cause a deflection of only theevaporant particles which are below a predetermined mass path apredetermined amount to cause deposition upon the substrate theparticles above said predetermined mass failing to impinge on saidsubstrate.

3. The method defined in claim 1 wherein said evaporant intercepts thesubstrate at an angle of substantially 90 with respect thereto.

4. The method of claim 1 wherein the evaporant is silicon monoxide.

5. The method of claim 1 wherein the gas is selected from a class whichdoes not react chemically with said evaporant.

6. The method of claim 1 wherein the gas reacts chemically with saidevaporant.

7. A method of forming thin film layers on a substrate which issubstantially free from defects comprising the steps of (a) positioninga source of material to be vaporized within a vacuum deposition chamber;

(b) positioning a substrate onto which the material is to condense outof direct line of sight of said source such that vapor particlesproduced by the heating of said material normally fail to impinge onsubstrate;

(0) heating said source to a temperature causing said material tovaporize; and

(d) introducing a suitable gas in a Well defined jet into said chamberat a location Where said gas ballistically deflects said vapor particlesbelow a predetermined size onto said substrate, the method being suchthat particles above said predetermined size fail to impinge on saidsubstrate.

8. The method as in claim 7 wherein said gas is chosen from the classincluding argon, Xenon, krypton, neon, helium and radon.

9. The method as in claim 7 wherein said gas is oxygen.

References Cited UNITED STATES PATENTS 2,831,784 4/ 1958 Gastinger117-406 2,920,002 1/1960 Auwarter 117-106 X 2,996,418 8/1961 Bleil117-106 X 3,113,040 12/1963 Winston 117-106 X 3,208,873 9/1965 Ames etal. 117-106 3,237,508 3/1966 Keller et al.

3,243,363 3/1966 Helwig 117-217 X OTHER REFERENCES IBM TechnicalDisclosure Bulletin, vol. 4, No. 6, December 1961, p. 6 relied upon.

ALFRED L. LEAVITT, Primary Examiner. A. GOLIAN, Assistant Examiner.

